Your Ultimate Guide

Finding the Right Envelope Size Made Easy

When it comes to shipping, finding the right envelope size is essential. Don't worry; we've got you covered! Below we delve into the world of envelope sizes, so you can make informed choices for your shipments. We'll explain the various envelope formats, their unique functions, and even introduce some lesser known but incredibly useful envelope types.

"C" in Envelope Sizing.

In envelope sizing, you may have noticed the use of letters like A, B, and C. The C envelope size is derived using the geometric mean of A and B sizes with the same number. This calculation results in a size that precisely fits the A size paper. For instance, calculating the geometric mean of A4 and B4 paper provides the dimensions of a C4 envelope, which flawlessly holds an A4 sheet of paper unfolded.

C NAME and Number SIZE IN MM (mm) STANDARD PAPER SIZE
C0 917 x 1297 A0 Sheet
C1 648 x 917 A1 Sheet
C2 458 x 648 A2 Sheet
C3 324 x 458 A3 Sheet
C4 229 x 324 A4 sheet, A3 sheet folded in half
C5 162 x 229 A5 sheet, A4 sheet folded in half
C6 114 x 162 A6 sheet, A4 sheet folded in four equal parts
C7 81 x 113 A7 sheet, A5 sheet folded in four equal parts
C8 57 x 81 A8 Sheet
C9 40 x 57 A9 Sheet
C10 28 x 40 A10 Sheet

Understanding the "C" Number Order.

If you've ever wondered why the 'C' numbers increase as the envelope sizes decrease, here's the explanation: Envelope sizing adheres to the ISO paper size system. So, a C5 envelope is designed to fit A5 paper, and a C4 envelope fits A4 paper. The ISO standard sizing works based on A0 paper, which is the largest size. The number alongside the A indicates the number of folds in half needed from an A0 sheet. For instance, A2 paper results from folding A0 twice, A3 from folding it thrice, and A4 from folding it four times. Hence, the number increases as it corresponds to the number of folds.

DL Envelope Size

The DL envelope (110mm x 220mm) is one of the most used envelope sizes for business and promotional purposes. Its versatility allows it to hold an A4 sheet folded into thirds or an A5 sheet folded in half. As such, the DL envelope is an ideal choice for sending business letters, invoices, brochures, and marketing materials. Its slim and professional appearance presents a polished image, making it suitable for corporate communications and direct mail campaigns. The DL envelope is often utilised by businesses for cost-effective mailings while maintaining a professional and organised look.

Common uses include: Business correspondence, marketing materials, and promotional mailings. Can hold an A4 sheet folded into thirds or an A5 sheet folded in half.

DL+ Envelope Size

The DL+ envelope (114mm x 229mm) offers a slightly larger size than the standard DL envelope, providing a bit more space for marketing materials, booklets, and catalogues. It is an excellent option when the standard DL size may feel too restrictive for promotional mailings or when the content requires a more spacious presentation. Its extended size allows businesses to deliver more comprehensive information while still adhering to the postal regulations for standard DL mailings.

Common uses include: Business correspondence, marketing materials, and promotional mailings. Can hold an A4 sheet folded into thirds or an A5 sheet folded in half.

C7 Envelope Size

The C7 envelope's small and compact size (82mm x 113mm) makes it perfect for personal and informal correspondence. It is commonly used for various intimate occasions, such as sending thank-you notes, RSVPs, and small invitations. Its charming dimensions add a touch of elegance to greeting cards and intimate messages between friends and family.

Common uses include: Perfect for holding A7-sized cards, invitations, and small notes.

C6 Envelope Size

The C6 envelope (114mm x 162mm) is a versatile and widely used envelope size suitable for various purposes. Its dimensions make it an excellent choice for sending A6-sized cards, postcards, and smaller documents. The C6 envelope is popular for personal correspondence, including birthday cards, holiday greetings, and thank-you notes.

Its compact size is also ideal for RSVP cards and announcements for special events.

Common uses include: Perfect for holding A6-sized cards, invitations, and small notes.

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C5 Envelope Size

The C5 envelope (162mm x 229mm) is an ideal choice for mailing A5-sized documents, brochures, and promotional materials. Its generous size allows it to hold unfolded A5 sheets comfortably, making it an excellent option for sending invitations, greeting cards, and small booklets. Businesses often use C5 envelopes for mailing marketing materials, event invitations, and product announcements.

Common uses include: Suitable for A5-sized documents and brochures. Often used for promotional materials, invitations, and greetings.

C4 Envelope Size

The C4 envelope (229mm x 324mm) is designed to hold unfolded A4-sized documents securely. As such, it is commonly used for business correspondence, official documents, and presentations. When sending important papers or proposals, the C4 envelope ensures that large documents remain flat and undamaged during mailing. Its size and capacity make it an efficient choice for businesses dealing with contracts, legal documents, and comprehensive reports.

Common uses include: Ideal for holding unfolded A4-sized documents, such as letters, contracts, and official documents. Often used for business correspondence.

C3 Envelope Size

The C3 envelope (324mm x 458mm) is a large-sized envelope primarily designed to hold unfolded A3 documents and other sizable materials. Due to its generous dimensions, it is commonly used for important business communications, such as sending large-scale presentations, proposals, and official documents. The C3 envelope ensures that your A3-sized materials remain flat and pristine during transit, making it an ideal choice for maintaining a professional appearance.

Common uses include: Larger items, posters, paintings and online e-commerce shipments.

Square Envelope Size

Square envelopes come in various sizes and offer a unique and visually appealing presentation for special occasions and creative projects. Commonly used for square-shaped cards, invitations Lempac offers them in standard sizes of 220 x 220mm and 165 x 165mm.

Common uses include: Business correspondence, marketing materials, and promotional mailings.

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Why is ISO Important When Considering Envelopes?

The International Organisation for Standardisation (ISO) plays a vital role in establishing uniformity and compatibility in envelope sizing worldwide. 

ISO envelope classification is primarily based on the ISO 216 standard which defines the international A series of paper sizes. This series is the most widely used and accepted across the globe, with A4 (210 x 297 mm) and A5 (148 x 210 mm) being the most common paper sizes. The international standard for envelopes is the C series (ISO 269) whose purpose is to accommodate the A paper sizes and are ideal for various purposes, such as business correspondence, official documents, and promotional mailings.

ISO classifies envelopes into B and C series but the most used is the C series envelopes which are tailored to accommodate A series paper sizes mainly without the need for folding, making them perfect for mailing unfolded documents.

The ISO standardisation is crucial for several reasons:

a. Global Consistency:
Having a unified envelope sizing system ensures that businesses and individuals across the world can communicate efficiently without worrying about size compatibility.

b. Printing and Manufacturing Efficiency:
With standardised envelope sizes, printing and manufacturing become more streamlined, leading to cost savings and reduced waste.

c. Postal Regulations Compliance:
Many postal services have guidelines on acceptable envelope sizes for specific postage rates. Adhering to ISO standards helps ensure your mailings meet these requirements, avoiding unnecessary delays or additional charges.

d. Brand Image and Professionalism:
Using standardised envelopes can enhance a company's professional image and brand consistency, both in domestic and international communications.

Envelope Sizes FAQ

Here are some commonly asked questions surrounding envelope sizes.

A quick and easy way to remember which envelope size you need is to swap the "A" letter of your paper size for the letter "C". For example, if you want an envelope to fit an A4 sheet of paper, then you'll need a C4 envelope (and so on).

Paper comes in A and B sizes. The C envelope size is the geometric mean of the A and B size of the same number. This calculation produces a size between the A and B dimensions to make an envelope to perfectly hold the A size paper. For example, if you calculate the geometric mean of A4 and B4 paper this will give you the dimensions of a C4 envelope (which is the ideal size to hold an A4 sheet of paper unfolded).

Yes, a C4 envelopes is larger than a C5 envelope. A C5 envelope is designed to fit A5 paper and a C4 envelope is designed to fit A4 paper. The ISO standard paper sizing system works by using A0 size paper as the base point and largest size. The number next to the A specifies the number of folds in half needed from an A0. For example, A2 paper is A0 folded twice, A3 paper is A0 folded 3 times, A4 paper is A0 folded 4 times. Therefore, the number increases as it relates to the number of folds.

The DL envelope originated in Germany in the 1920's and was then known as DIN Lang, however these days DL is known to stand for 'Dimension Lengthwise”. A DL envelope is designed to fit an A4 piece of paper, folded into thirds. This is one of the most common envelope sizes for business letters and you will find much of your standard post arrives in a DL size envelope.